Bug #15608: What should be the correct output for Method#inspect with singleton methods?

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 2.6.1p33 (2019-01-30 revision 66950) [x86_64-linux]
• Backport: 2.5: REQUIRED, 2.6: DONE, 2.7: DONE
• Tags: core, patch

[Eregon (Benoit Daloze)]

bug.rb:

class C
  def foo
  end
end

obj = C.new

class << obj
  alias bar foo
end

p obj.method(:foo).owner
p obj.method(:foo)
raise unless obj.method(:foo).owner == C

p obj.method(:bar).owner
p obj.method(:bar)
raise unless obj.method(:bar).owner == obj.singleton_class

$ chruby 2.0.0
$ ruby -v bug.rb 
ruby 2.0.0p648 (2015-12-16) [x86_64-linux]
C
#<Method: C#foo>
#<Class:#<C:0x0055b39fcd2c30>>
#<Method: C(C)#foo>

$ chruby 2.3.8
$ ruby -v bug.rb 
ruby 2.3.8p459 (2018-10-18 revision 65136) [x86_64-linux]
C
#<Method: C#foo>
#<Class:#<C:0x000055668ebef268>>
#<Method: #<C:0x000055668ebef268>.bar(foo)>

$ chruby 2.4.5
$ ruby -v bug.rb 
ruby 2.4.5p335 (2018-10-18 revision 65137) [x86_64-linux]
C
#<Method: #<C:0x000055fdc99dc908>.foo>
#<Class:#<C:0x000055fdc99dc908>>
#<Method: #<C:0x000055fdc99dc908>.bar(foo)>

Same for 2.5.3 and 2.6.1

I think Method#inspect should show on which Module the method is defined (Method#owner), and only singleton methods should be shown as receiver.method, so:

C
#<Method: C#foo>
#<Class:#<C:0x000055668ebef268>>
#<Method: #<C:0x000055668ebef268>.bar(foo)>

Which only Ruby 2.3 does interestingly.

---

What's the meaning of the C1(C2) notation?

It seems to show "#{receiver.class}(#{owner}) or "#{receiver.singleton_class if receiver has a sclass} depending on the version:

class D < C
end
d = D.new
p d.method(:foo)
d.singleton_class
p d.method(:foo)

2.0-2.3:
#<Method: D(C)#foo>
#<Method: D(C)#foo>
2.4-2.6:
#<Method: D(C)#foo>
#<Method: #<D:0x000055c12b45e218>.foo>

I think the Ruby 2.4+ behavior is confusing and incorrect here, the object shouldn't be shown if it's not a singleton method, and Method#inspect shouldn't change for a given method.

Do you agree what I describe should be the correct behavior?
Can we fix it then?

[Eregon (Benoit Daloze)]

• Description updated (diff)

[Eregon (Benoit Daloze)]

• Description updated (diff)

[Eregon (Benoit Daloze)]

• Description updated (diff)

[Eregon (Benoit Daloze)]

It would be great to have specs under spec/ruby for this, and that could explain the rationale behind each decision for each case.
Unit tests do not achieve that.

[wanabe (_ wanabe)]

Current behavior is from r60127.
I guess it will come to the same to replace data->klass of method_inspect() to data->iclass.

[jeremyevans0 (Jeremy Evans)]

• File method-inspect-15608.patch method-inspect-15608.patch added

Attached is a patch that fixes this issue. @wanabe (_ wanabe) was correct that we need to use data->iclass if available. However, changing just that breaks some existing tests. To keep existing tests working but also fix this issue, if the object has a singleton class, but the method was not defined on the singleton class, continue to use data->klass, but skip the singleton class and included modules.

Example:

class C
  def foo
  end
end
class D < C
end
d = D.new
p d.method(:foo)
d.singleton_class
p d.method(:foo)

Result after patch:

#<Method: D(C)#foo t/t7.rb:2>
#<Method: D(C)#foo t/t7.rb:2>

[Eregon (Benoit Daloze)]

Thanks for the patch.
What tests does it break, could you copy the output?
The tests might be wrong too.

[jeremyevans0 (Jeremy Evans)]

Eregon (Benoit Daloze) wrote:

What tests does it break, could you copy the output?

I didn't keep the output. From a brief analysis, it appeared to be to be tests that you wouldn't want to break. Using data->iclass instead of data->klass results in C#foo instead of D(C)#foo for D.new.method(:foo).

[jeremyevans0 (Jeremy Evans)]

I rebased my patch against the current master branch and added a pull request for it: https://github.com/ruby/ruby/pull/2949

[jeremyevans0 (Jeremy Evans)]

• Status changed from Open to Closed

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN to 2.4: UNKNOWN, 2.5: REQUIRED, 2.6: REQUIRED

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 2.4: UNKNOWN, 2.5: REQUIRED, 2.6: REQUIRED to 2.5: REQUIRED, 2.6: REQUIRED, 2.7: REQUIRED

[naruse (Yui NARUSE)]

• Backport changed from 2.5: REQUIRED, 2.6: REQUIRED, 2.7: REQUIRED to 2.5: REQUIRED, 2.6: REQUIRED, 2.7: DONE

ruby_2_7 0d24fb774d84d4a99454ce10fd343da00049a588.

[usa (Usaku NAKAMURA)]

• Backport changed from 2.5: REQUIRED, 2.6: REQUIRED, 2.7: DONE to 2.5: REQUIRED, 2.6: DONE, 2.7: DONE

Backported into ruby_2_6 at r67902.